Symbiosis: Entoprocta (comensal)

Ophiuroidea – Entoprocta

• Ophiuroidea: Ophioplinthus gelida: host 
• Entoprocta: Loxosomella sp : commensal

Loxosomella sp. as commensal of Ophioplinthus gelida (Koehler 1900), from which it obtains a substrate that provides its mobility to the food sources, the advantage of not being buried by the sediment as well as certain protection from predators Emschermann (1993). For Ophioplinthus it seems to be no benefits at all.

Loxosomella is mainly located at the edges of dorsal interradii as well as on the lateral plates along the arms, being able to appear with a high density of individuals. They can also appear on the ventral part of the disk, but in a scarce proportion.

Entoprocta (Kamptozoa): colonial or solitary suspensivore lophophorates whith the anus inside of the tentacle crown (lophophore), unlike the bryozoans (Ectoprocta) Loxosomella are solitary entoprocts.

1. Extended lophophorate   2. Bud    3. Contracted lophophorate

Materials studied from Expedition ANTARKTIS- XXlll / 8 Polarstern 2006/2007  in  Joinville Island (3 brittle stars with Loxosomella). They correspond to the same geographical area that the specimens studied by Emschermann to Loxosomella antarctica (Weddell Sea and Bransfield strait).

Specimen conserved in 70% ethanol, all  photographs were made in ethanol.

Collected by Pablo J. González-López.

Identified by Rafael Martín-Ledo.
The study was made using Motic SMZ-168 TL stereo microscope.

References

Emschermann (1993) On antarctic Entoprocta: Nematocyst-like organs in a loxosomatid, adaptive developmental strategies, host specificity, and bipolar occurrence of species. Biol. Bull 184: 153-185

July 2010

Symbiosis: Ophioplinthus - Ascothorax (parasitism)

Ophioplinthus brevirima: Host
Ascothorax sp: endoparasite

Inside there were several parasites (Ascothorax sp) with globose aspect; the smaller ones (probably males) with better distinguished morphology having two valve, while the larger specimens are possibly females. This difference in size, and better conservation of structures in male specimens is a common phenomenon in many parasitic crustaceans.

Ophioplinthus brevirima has short genital  slits, hence its specific epithet. In the studied specimens one of the slits, which coincides with the deformed area of the disc has a deformation making it larger, and the proximate plates look abnormal. It is likely had been caused when the endoparasites were leaving their host.

This is supposedly the first record of endoparasites for Ophioplinthus brevirima.

Materials studied from Expediton ANTARKTIS-XXIII/8 Polarstern 2006/2007 in Snow Hill and Dundee Islands. Specimens conserved in 70% ethanol, all photography were made in ethanol using Motic SMZ-168 TL  stereo microscope.
Collected by Pablo J. González-López
Identified by Rafael Martín-Ledo
July 2010

Live Ophioplinthus brevirima, covered by Iophon sponge

Symbiosis: Hydrozoa (mutualist)

Ophiuroidea – Hydrozoa

Ophioplinthus relegata : mutualist symbiont
Hydractinia sp : mutualist symbiont

Ophioplinthus relegata (Koehler) with Hydractinia sp

One of the most beautiful symbiosis observed in the brittle stars is that of an ophiuroid covered with “flowers” (although they are carnivorous). The colonial hydrozoan Hydractinia vallini Jaederh places its hydrorhiza and polyps between and over the plates of Ophioplinthus relegata (Koehler, 1922).

1. Gastrozooids     2. Gonozooid     3. Hydrorhiza

Polyps, gastrozooids with their tentacles and globose gonozooids are located  mainly in the periphery of the disc and on the side parts of the arms.
The hydrorhizas are situated between interventrales plates, as well as in the characteristic jaw depression of  Ophioplinthus relegata, which also can give a shelter to a polyp. The dorsal part of the disk is generally free.

For Svoboda et al (1997), the ophiuroid transports the hydractinia to the new food resources and keeps it away from the sediment that would collapse it, while the hydractinia defends the brittle star from potential predators, which is similar to the symbiosis of gastropods with cnidarians, a mutualistic type of relationship.

1. Gastrozooid   2. Gonozooid   3. Hydrorhiza

In excavated jaw area of some specimens appear polyps which are larger than the rest of polyps presented in the same ophiuroid. Such specimens have very few polyps in the areas where they normally are, such as the periphery of the disc. The proximity to the mouth of the brittle star induces me to think that hydroids can feed on the remains of the food that fall off when the ophiourid is eating (commensalism), or even that it could be a case of kleptoparasitism.

Specimens conserved in 70% ethanol, all  photographs were made in ethanol.

Collected by Pablo J. González-López. Cruiser ANTARKTIS XXIII/8  Polarstern

Identified by Rafael Martín-Ledo.
The study was made using Motic SMZ-168 TL stereo microscope.

References

Svoboda S, Stepanjants S, Smirnov I (1997) Two polar Hydractinia species (Cnidaria), epibiotic on two closely related brittle stars (Echinodermata): an example for a taxonomic and ecological bipolarity. Antarctic communities: species, structure, and survival edit Battaglia B ,Valencia J, Walton DWH Scientific Committee on Antarctic Research 22

July 2010

Pycnogonid on Ophioplinthus

This morning, after a delicious breakfast at Vicente’s, I was in my laboratory ready to observe specimens, when I suddenly found a beautiful composition: a pycnogonid (Austrodecus sp) grasping the spicules of the Iophon sponge which covers the disk of a Ophioplinthus gelida.

The pycnogonids, sea spiders, are marine arthropods that feed mainly on hydroids, bryozoans, anemones and other soft-bodied animals in which insert their proboscis to suck their fluids. In Antarctic waters there are about 175 species, which amounts to be 18% of the pycnogonids on a world scale.

Hardly any brittle star can be found among their prey because of having the body covered with calcareous plates which, like an armor-plate, may dissuade many predators who are not armed with appropriate dentition or stylet (pricker).

So, this picture might seem to be a portrait of a process of micropredation or even ectoparasitism, but I tend to consider it just an accident, although there can appear a supposition that what the pycnogonid might have been really looking for could have been the abundat offspring of gemmules of the Iophon sponge.

Specimens conserved in 70% ethanol, all  photographs were made in ethanol.

Collected by Pablo J. González-López. Cruiser ANTARKTIS XXIII/8  Polarstern

Identified by Rafael Martín-Ledo
The study was made using Motic SMZ-168 TL stereo microscope.

March 2010

Symbiosis: Protozoa - Ciliophora- (epibiont)

Ophiuroidea – Protozoa (Ciliophora)

• Ophiuroidea: Ophioplinthus gelida: host
• Protozoa: Folliculina sp: epibiont

On the surface of some samples of Ophioplinthus gelida may appear numerous specimens of ciliate Folliculina sp. Their presence on the ophiuroid is mostly in the radial shields, but they may also appear on any dorsal disc plate and on the dorsal and lateral arm plates. Their arrangement is both solitary and in groups of several individuals, Andrews (1914).

This relationship is an epibiosis, possibly facultative Wahl & Mark (1999). This inquilinism does not seem to affect the brittle star, while the protozoa are provided with food availability, with protection from potential predators and are save from being buried in the bottom sediments.

Specimens conserved in 70% ethanol, all  photographs were made in ethanol.

Collected by Pablo J. González-López. Cruiser ANTARKTIS XXIII/8  Polarstern

Identified by Rafael Martín-Ledo.
The study was made using Motic SMZ-168 TL stereo microscope.

References

Andrews E A 1914 The Bottle – animalcule, Folliculina oecological notes.  Biol Bull  26: 245-315

Koehler R (1922) Echinodermata Ophiuroidea. Adelaide: Australas Antarct Exped (1911–1914) Sci Rep Ser C Zool Bot 8:1–98

Madsen FJ (1967) Ophiuroidea. B.A.N.Z. Antarctic Research Expedition (1929–1931) under the Command of Sir Douglas Mawson Rep Ser B 9:123–145

Mortensen T (1936) Echinoidea and Ophiuroidea. Discovery Reports, National Institute of Oceanography Cambridge 12:199–348

Wahl M & Mark O (1999) The predominantly facultative nature of epibiosis: experimental and observational evidence. Mar Ecol Prog Ser Vol. 187: 59-66

July 2010

Roofs and eyeglasses in Antarctic ophiuroids

In 1961 Fell, in his monograph on the Ross Sea Ophiuroidea, drew attention to the development of skeletal excrecence in Antarctic ophiuroids from Euvondrea and Ophiosteira genera. Fell found no explaination for these outgrowths.

These expansions, especially in the dorsal arm plates, can also be seen in other Antarctic species such as Ophiura (Ophiuroglypha) carinifera, Anophiura banzarei, Ophiomages cristatus, Ophiomastus bispinosus and some species of Ophioplinthus genus.

Ignoring the mere evolutionary whim, there could be various interpretations. For example, passive defense: the protrusive elements could dissuade the predators which would prefer something easier to chew and swallow. Or, acting as peaked roofs somewhere in Siberia or Pirinei Mountains –  little flat surface on aboral part protects them from heavy “snowfalls” and, so, doesn’t let them be buried in funds with a high degree of sedimentation. Or, the explanation could be the possible presence of amplifier lenses for photoreception (see symmetrical structures as honeycomb cells of Ophiosteira).

At any rate, nature manifests its spectacularity through the tiniest details of organisms which did not evolve to amaze us, nonetheless, we can’t help being marvelled at them.

November 2011

Symbiosis: Nematoda (parasitism)

Ophioplinthus / Ophionotus - Nematoda

Ophioplinthus gelida (Koehler, 1901): host
Ophionotus victoriae Bell, 1902: host
Nematoda (unidentified): coelomic cavity and bursae endoparasites 

Nematodes identified as parasites of Antarctic ofiuroids belong to Thalassonema genus; they have been found in Ophiocten amitinum, although mentioned in sub-Antarctic waters, and in Ophiacantha antarctica. Mortensen 1936, cites the presence of nematodes, unidentified, in Amphiura microplax disjunta.

  


Nematodes, in some cases, can be seen going out from the openings in the disc and, on opening some ofiuroids, several nematodes can be seen spread all over the body cavity.

References

Jangoux M (1987) Diseases of Echinodermata. II: Agents metazoans (Mesozoa to Bryozoa) Dis aquat org, vol. 2: 205-234

Mortensen T (1936) Echinoidea and Ophiuroidea. Discovery Reports, National Institute of Oceanography Cambridge 12:199–348

Collected by Pablo J. González-López. Cruiser ANTARKTIS XXIII/8  Polarstern.
The study was made using Motic SMZ-168 TL stereo microscope.

July 2010